[gentoo-user] The sudden disappearance of ....WHAT??? (I/O error on a SD flash card?!)

Hi,

(Running Gentoo Linux on a 4.9.17 vanilla (ftp.kernel.org) Linux
kernel)

I was doing a backyp of a 64GB SAMSUNG flash card to my
harddisk....which runs for quite a while...

For that I mount the partitions and tarred their contents as root
to the harddisk

Syddenly out of nothing/from nowhere/into thin air or whatever:
read errors happens and the process stops.

First I thought of the one an most hated failure of harddisks, which
in years of deveopment of computer technology no company was able to
fix: No space left on device.

But - no,,,the error was a _READ_ error and a 'ls' of the mountpoints
show....nothing but empty directories.

I tried to unmount/remount the sd card and got this output:
mount: wrong fs type, bad option, bad superblock on /dev/sdb2,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.

dmesg gives me:
[  236.021878] UDF-fs: warning (device sdb2): udf_fill_super: No partition found (2)


UDF??? --  Those partitions are either ext4 or vfat.
(A tried that with and without the -t option...)

fdisk -l /dev/sdb gave me:
Device     Boot     Start       End  Sectors  Size Id Type
/dev/sdb1           32768  73433087 73400320   35G 83 Linux
/dev/sdb2        73433088 100696063 27262976   13G 83 Linux
/dev/sdb3       100696064 125042687 24346624 11.6G 83 Linux

So -- the partition table is still there (I had booted the PC
in between...so these are no ghosts of an abondomed cache...)

If a certain kernel module woyld be missing I wouldn't not
able to mount the partition right before starting the backyp
- but I could.

The partition table is there so this part of "DMESG predicts"
is also not applicable here.

What happens here? Flash killed? Is there any chance to rescye
some or all contents of that card? Any ideas other than
hoping for an alternate reality?

Thanks a lot for any help in advance!

Cheers
Meino